I did a little searching, so you might not have to start from scratch.

I found 2 things
First, an expensive solution
http://www.imeg.com/jadtech/c100spec.htm

Next, a project that may be of some use.  This project has a circuit design
available and software for capturing data from a legacy device that uses a
printer. I don't know if you want this data for a PC or for a PIC.  But the
circuit should be useful
http://home.clear.net.nz/pages/kheidens/lptcap/lptcap.htm

Hope this helps,
Giles

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